Design and optimization of pin fin heat sinks for low velocity applications

In a number of electronic cooling applications, the air flow velocity and direction are not very well defined or controlled. In these applications, pin fin heat sinks are widely used because they are not sensitive to air flow direction. A study was undertaken to optimize the design of pin fin heat sinks for use in low velocity applications where there is plenty of open space around for the air to bypass the heat sink, if it encounters high pressure drop across it. The goal of this study was to maximize the thermal performance and keep the design such that it is easily manufacturable to keep the cost low. A special test fixture using a heat flux meter was designed to test the heat sinks for thermal performance. Several aluminum pin fin heat sinks having a 25×25 mm base size, heights from 5 to 25 mm, pin arrays of 4×4 to 8×8, and pin fin cross sections from 1.5×1.5 mm to 2.5×2.5 mm were fabricated and tested for thermal performance. Some of the commercial aluminum heat sinks with various surface finishes (such as black anodized, gold chromated, clear anodized and untreated) were also evaluated to determine the effect of surface treatment on thermal performance. The heat sink tester and the test data for the heat sinks used in this optimization study are reviewed in this paper. The results show that it is possible to design an optimum pin fin heat sink for any flow situation. However, it is not realistic to have several heat sink designs to cover various applications. In low velocity (about 1 m/s or less) open flow situations, the best compromise for pin fin heat sink with about 25×25 mm base size and heights up to 15 mm is the 6×6 pin fin configuration with fin cross-sections of 1.5×1.5 mm